i was under the impression that 'INDRA' was a title, not a person. different ppl became INDRA at different times. proly no term limits on the title, but im guessing that as a person became indra longer, they got more and more decadent and careless, and eventually some dude with enough 'tapasya power' or some asur with a large enuff army would come along, take over, and voila, a new INDRA